1. FIELD OF THE INVENTION
This invention relates to an electrical connector. More particularly, the invention is an electrical connector for establishing electrical contact between two or more flexible circuits and at least one other circuit device.
2. DESCRIPTION OF THE RELATED ART
Conventional methods of interconnecting electrical or electronic circuit components consist of the use of separate connector structures and/or soldering terminals on the components to conductors which deliver current to or from the components. While generally suitable for its intended purposes, interconnecting electrical components via separate connector structures does suffer from certain drawbacks and deficiencies including high manufacturing and purchasing costs during installation and connection. Similarly, soldering terminals is undesirable as the substrate which supports an exposed terminal must be able to withstand relatively high temperatures with no adverse effects. Also, soldering connections can be time consuming and therefore be labor intensive and expensive. Another problem with soldered connections is the relative difficulty in disconnecting a soldered terminal during repairs and manufacturing. Finally, such electrical connectors simply cannot provide adequate isolation between circuit traces in applications specifying very tightly spaced circuit traces, such as those required to connect multitrack magnetic tape heads to the remaining components of a tape drive. An example of such is the 18 track magnetic tape head in the IBM 3490 Tape Drive. As track densities increase in the future, the need for alternative connectors also increases.
In some applications it has been found desirable to replace the use of separate connecting structures and/or soldering as a technique for use in establishing connections to flexible and other circuits. In these, applications, the requisite electrical contact may be established by mechanically pressing the terminal portions of the circuit against terminal pads on the connector, device or another circuit. Such pressure connections are customarily made with the aid of a resilient pressure applicator, such as an elastomeric member, which is placed in compression to bias at least one of the components to be electrically interconnected toward the other component to hold the terminal portions thereof in electrical contact.
An example of the aforementioned solderless connection system is disclosed in U.S. Pat. No. 4,468,074, hereby incorporated by reference. This patent discloses an apparatus wherein contact portions of a first array of conductive elements are urged against mating contacts of a second array of conductive elements by a pressure applicator comprising a resilient cellular plastic material thereby establishing and maintaining an electrical connection therebetween. The use of such a cellular resilient material permits a plurality of closely spaced exposed electrical conductors on or extending from a pair of substrates to be aligned and thereafter reliably pressed together, with the electrical connections being established by a requisite contact pressure applied to the substrates. Such a solderless connector may be employed to interconnect flexible circuits, to connect flexible circuits on rigid substrates, to establish connections between the leads extending from integrated circuits in a circuit pattern on a flexible or rigid circuit board, and in other applications.
Other solderless connectors are disclosed in U.S. Pat. Nos. 4,647,125, 4,655,524, 4,691,972, 4,717,345, 4,744,764, 4,538,885, 4,770,645, 4,832,609, all of which are cited in U.S. Pat. No. 4,913,656. Additional flexible circuit connectors using resilient materials are disclosed in U.S. Pat. Nos. 4,768,971, 4,695,258, 3,977,756. Other flexible circuit connectors are disclosed in U.S. Pat. Nos. 3,795,885, 4,871,315, 2,981,918, 4,808,112, and 4,116,516 and in the IBM Technical Disclosure Bulletin--Miller, Connector for Multilayer Circuit Package, Vol. 15, No. 5, October, 1972, pp. 1614-15 and Blackwell et al, Flexible Tape Cable Connection, Vol. 18, No. 11, April, 1976, p. 3830.
It will be appreciated that at least some of the aforementioned references disclose solderless connectors for connecting a flexible circuit and another flexible or rigid circuit device. However, there are many applications requiring at least two flexible circuits to be connected to a third flexible or rigid circuit device. A connector for such an application is disclosed in U.S. Pat. No. 4,913,656, hereby incorporated by reference. The connector disclosed uses a non-wiping, pressure-mated connection in a package with allowance for very tight tolerances on pad width and spacing, yet allowing for easy assembly and disassembly. Two flexible circuits are mounted to a clamp plate subassembly with the other circuit device located on a separate clamp backer plate. The sub-assembly includes a top clamp plate and a central circuit block having a longitudinal slot therethrough. The flexible circuits are sandwiched between the top clamp plate and the circuit block. One flexible circuit extends through the slot and is folded about the circuit block, trapping a resilient pressure pad between the end of the flexible circuit and the circuit block, to expose contact pads at the end of the flexible circuit. The other flexible circuit does not extend through the slot, but instead wraps about a longitudinal edge of the circuit block to similarly trap a resilient pressure pad and expose contact pads. The sub-assembly thus locates the flexible circuits in the appropriate area and provides an elastomeric pressure member in the contact area. The sub-assembly also provides strain relief for the flexible circuits to protect the contact area both before and after connection. The assembled connector is held in the assembled position with two screws tightened to where the hardware parts engage "stops" protecting the clamp from bowing, but allowing high enough torque on the fasteners to resist subsequent vibration. Although the connector disclosed in U.S. Pat. No. 4,913,656 does mate two or more flexible circuits to a third circuit device, it nevertheless has certain previously unrecognized drawbacks. One problem is the use of a single piece circuit block with a longitudinal slot therein. Such a circuit block requires that one of the flexible circuits be inserted through the slot during assembly (and folded, as described previously), resulting in significant scrap/rework costs when a flexible circuit is damaged during the insert and fold operations. In addition, pins extending from the circuit block are used to align and maintain the folded and wrapped flexible circuits on the circuit block. The flexible circuits of preformed radius must be stretched out of shape and wrapped over the pins, for alignment resulting in further scrap/rework.
Another problem with the aforementioned connector is related to the sub-assembly. Because the sub-assembly includes a top clamp plate and a circuit block sandwiching the flexible circuits, strain relief must be provided to allow for handling of the sub-assembly without damage thereto. Yet another problem is the location of the resilient pressure pads between the circuit block and the flexible circuits. The resilient pressure pads are used to apply constant pressure across the entire span of closely spaced electrical contacts to ensure that each pair of such contacts properly mate. The resilient pressure pads should thus be located on the side of the electrically mated contacts which is most compliant. Where the third circuit device is itself a flexible circuit, particularly one being more compliant than the first two flexible circuits, the resilient pressure pads are not optimally located on the side of the third flexible circuit.